Chronic Vs. Acute ACL Tears: Impact of Surgical Timing on Quadriceps Strength

Quadriceps strength plays a large role in returning patients to pre-injury function after an anterior cruciate ligament (ACL) reconstruction. Yet little was known about the impact of surgical timing on strength.

“We wanted to be able to tell patients what to expect in terms of preoperative quadriceps strength and the progression of quadriceps strength postoperatively based on whether they have an acute or chronic ACL tear,” says Rachel Slaven, PT, DPT, a physical therapist at Shelbourne Knee Center.

Study Methods

Slaven and Bauman retrospectively reviewed data on 2,829 Shelbourne Knee Center patients (1,178 females; 1,651 males) who underwent ACL reconstruction using a contralateral patellar tendon graft from 1994 to 2020.1 Patients were separated based on the time from injury to surgery (acute ≤ 4 months and chronic ≥ 6 months). The average time from injury to surgery was 1.7 months for the acute group and 19.3 months for the chronic group.

All patients participated in a preoperative rehabilitation protocol focused on range of motion, gait, leg control and swelling. Postoperatively, patients followed the protocol developed by Shelbourne et al., including full weight bearing, early return of full extension/flexion equal to the opposite side and swelling reduction.2

Data included:

  • Isokinetic strength testing at 180°/seconds and 60°/seconds for strength:
    • Preoperatively
    • Postoperatively at 1, 2, 3, 4, 6, 9 and 12 months
  • Preoperative strength:
    • A ratio of involved side compared to uninvolved side
  • Time to return to preoperative strength:
    • Days required to achieve strength ≥ 90% of preoperative leg strength.

Chronic Tears: Better Strength

“We found that people who had chronic ACL tears actually went into surgery with better preoperative strength and were able to achieve strength faster postoperatively compared to those with acute ACL tears,” says Slaven. Study results show statistically significantly better results for chronic than acute ACL reconstruction patients for:

  • Preoperative strength
  • Time to return to preoperative strength
  • Strength 1 month postoperatively.

Thus, consideration of surgical timing of ACL reconstruction as it relates to the return of quadriceps strength is important. Surgical timing does not impact the progression of limb symmetry postoperatively.

Slaven, Bauman and the other physical therapists at Shelbourne Knee Center regularly conduct and present their own research studies, and also participate in the center’s overall research program. They submitted this study to the Combined Sections Meeting of the American Physical Therapy Association (APTA), the APTA-sponsored Indiana and Kentucky Combined Fall Conference, and the American Association of Orthopedic Surgeons. The planning committees for these meetings will be reviewing the submissions over the next few months.

2 Time to Return to Preoperative Strength Chart


  1. Slaven R, Bauman S. The effects of surgical timing on preoperative and postoperative quadriceps muscle strength following an anterior cruciate ligament reconstruction. 2020. Abstract.
  2. Shelbourne KD, Nitz P. Accelerated rehabilitation after anterior cruciate ligament reconstruction. Am J Sports Med. 1990;18(3):292-299.